What you experienced could have been (as I'm sure you know) any one of the possibilities you've named.
I can't think of any odd experience I've had, though I know I've had some. Honestly, though, when I was reading your post my mind flashed to a dream I had some years ago about being alone in a large, multi-level gym. The lights were off; only the sunlight was coming through panels on the roof. Your experience reminded me of that dream. Go figure!